4,342 research outputs found
The FORS1 catalogue of stellar magnetic field measurements
The FORS1 instrument on the ESO Very Large Telescope was used to obtain
low-resolution circular polarised spectra of nearly a thousand different stars,
with the aim of measuring their mean longitudinal magnetic fields. A catalogue
of FORS1 magnetic measurements would provide a valuable resource with which to
better understand the strengths and limitations of this instrument and of
similar low-dispersion, Cassegrain spectropolarimeters. However, FORS1 data
reduction has been carried out by a number of different groups using a variety
of reduction and analysis techniques. Our understanding of the instrument and
our data reduction techniques have both improved over time. A full re-analysis
of FORS1 archive data using a consistent and fully documented algorithm would
optimise the accuracy and usefulness of a catalogue of field measurements.
Based on the ESO FORS pipeline, we have developed a semi-automatic procedure
for magnetic field determinations, which includes self-consistent checks for
field detection reliability. We have applied our procedure to the full content
of circular spectropolarimetric measurements of the FORS1 archive. We have
produced a catalogue of spectro-polarimetric observations and magnetic field
measurements for about 1400 observations of about 850 different objects. The
spectral type of each object has been accurately classified. We have also been
able to test different methods for data reduction is a systematic way. The
resulting catalogue has been used to produce an estimator for an upper limit to
the uncertainty in a field strength measurement of an early type star as a
function of the signal-to-noise ratio of the observation. While FORS1 is not
necessarily an optimal instrument for the discovery of weak magnetic fields, it
is very useful for the systematic study of larger fields, such as those found
in Ap/Bp stars and in white dwarfs.Comment: Accepted for publication by A&
Induced gravitational collapse at extreme cosmological distances: the case of GRB 090423
CONTEXT: The induced gravitational collapse (IGC) scenario has been
introduced in order to explain the most energetic gamma ray bursts (GRBs),
Eiso=10^{52}-10^{54}erg, associated with type Ib/c supernovae (SNe). It has led
to the concept of binary-driven hypernovae (BdHNe) originating in a tight
binary system composed by a FeCO core on the verge of a SN explosion and a
companion neutron star (NS). Their evolution is characterized by a rapid
sequence of events: [...]. AIMS: We investigate whether GRB 090423, one of the
farthest observed GRB at z=8.2, is a member of the BdHN family. METHODS: We
compare and contrast the spectra, the luminosity evolution and the
detectability in the observations by Swift of GRB 090423 with the corresponding
ones of the best known BdHN case, GRB 090618. RESULTS: Identification of
constant slope power-law behavior in the late X-ray emission of GRB 090423 and
its overlapping with the corresponding one in GRB 090618, measured in a common
rest frame, represents the main result of this article. This result represents
a very significant step on the way to using the scaling law properties, proven
in Episode 3 of this BdHN family, as a cosmological standard candle.
CONCLUSIONS: Having identified GRB 090423 as a member of the BdHN family, we
can conclude that SN events, leading to NS formation, can already occur already
at z=8.2, namely at 650 Myr after the Big Bang. It is then possible that these
BdHNe originate stem from 40-60 M_{\odot} binaries. They are probing the
Population II stars after the completion and possible disappearance of
Population III stars.Comment: 9 pages, 9 figures, to appear on A&
A common behavior in the late X-ray afterglow of energetic GRB-SN systems
The possibility to divide GRBs in different subclasses allow to understand
better the physics underlying their emission mechanisms and progenitors. The
induced gravitational collapse scenario proposes a binary progenitor to explain
the time-sequence in GRBs-SNe. We show the existence of a common behavior of
the late decay of the X-ray afterglow emission of this subclass of GRBs,
pointing to a common physical mechanism of their late emission, consistent with
the IGC picture.Comment: 3 pages, to appear in the proceedings of the Gamma-Ray Burst
Symposium 2012 - IAA-CSIC - Marbella, editors: Castro-Tirado, A. J.,
Gorosabel, J. and Park, I.
A Mission to Explore the Pioneer Anomaly
The Pioneer 10 and 11 spacecraft yielded the most precise navigation in deep
space to date. These spacecraft had exceptional acceleration sensitivity.
However, analysis of their radio-metric tracking data has consistently
indicated that at heliocentric distances of astronomical units,
the orbit determinations indicated the presence of a small, anomalous, Doppler
frequency drift. The drift is a blue-shift, uniformly changing with a rate of
Hz/s, which can be interpreted as a
constant sunward acceleration of each particular spacecraft of . This signal has become known as the Pioneer
anomaly. The inability to explain the anomalous behavior of the Pioneers with
conventional physics has contributed to growing discussion about its origin.
There is now an increasing number of proposals that attempt to explain the
anomaly outside conventional physics. This progress emphasizes the need for a
new experiment to explore the detected signal. Furthermore, the recent
extensive efforts led to the conclusion that only a dedicated experiment could
ultimately determine the nature of the found signal. We discuss the Pioneer
anomaly and present the next steps towards an understanding of its origin. We
specifically focus on the development of a mission to explore the Pioneer
Anomaly in a dedicated experiment conducted in deep space.Comment: 8 pages, 9 figures; invited talk given at the 2005 ESLAB Symposium
"Trends in Space Science and Cosmic Vision 2020", 19-21 April 2005, ESTEC,
Noordwijk, The Netherland
The broad-line type Ic SN 2020bvc: signatures of an off-axis gamma-ray burst afterglow
Long-duration gamma-ray bursts (GRBs) are almost unequivocally associated
with very energetic, broad-lined supernovae (SNe) of Type Ic-BL. While the
gamma-ray emission is emitted in narrow jets, the SN emits radiation
isotropically. Therefore, some SN Ic-BL not associated with GRBs have been
hypothesized to arise from events with inner engines such as off-axis GRBs or
choked jets. Here we present observations of the nearby ( Mpc) SN
2020bvc (ASAS-SN 20bs) which support this scenario. \textit{Swift} UVOT
observations reveal an early decline (up to two days after explosion) while
optical spectra classify it as a SN Ic-BL with very high expansion velocities
( 70,000 km/s), similar to that found for the jet-cocoon emission in
SN 2017iuk associated with GRB 171205A. Moreover, \textit{Swift} X-Ray
Telescope and \textit{CXO} X-ray Observatory detected X-ray emission only three
days after the SN and decaying onwards, which can be ascribed to an afterglow
component. Cocoon and X-ray emission are both signatures of jet-powered GRBs.
In the case of SN 2020bvc, we find that the jet is off axis (by 23
degrees), as also indicated by the lack of early ( day) X-ray
emission which explains why no coincident GRB was detected promptly or in
archival data. These observations suggest that SN 2020bvc is the first orphan
GRB detected through its associated SN emission.Comment: 9 pages, 6 figures, 5 tables. Accepted for publication in A&
Letter of Intent: Muonium R&D/Physics Program at the MTA
With the planned turn-on of the PIP-II 800 MeV superconducting proton linac,
Fermilab will potentially become the world's best laboratory at which to carry
out fundamental muon measurements, sensitive searches for symmetry violation,
and precision tests of theory. In preparation, we propose to develop the
techniques that will be needed. An R&D and physics program is proposed at the
Fermilab MeV Test Area to use the existing 400 MeV Linac to demonstrate the
efficient production of a slow muonium beam using stopped in a
~100-m-thick layer of superfluid helium, and to use that beam to measure
muonium gravity.Comment: 3 pages, submitted to Fermila
GAME: Grb and All-sky Monitor Experiment
We describe the GRB and All-sky Monitor Experiment (GAME) mission submitted
by a large international collaboration (Italy, Germany, Czech Repubblic,
Slovenia, Brazil) in response to the 2012 ESA call for a small mission
opportunity for a launch in 2017 and presently under further investigation for
subsequent opportunities. The general scientific objective is to perform
measurements of key importance for GRB science and to provide the wide
astrophysical community of an advanced X-ray all-sky monitoring system. The
proposed payload was based on silicon drift detectors (~1-50 keV), CdZnTe (CZT)
detectors (~15-200 keV) and crystal scintillators in phoswich (NaI/CsI)
configuration (~20 keV-20 MeV), three well established technologies, for a
total weight of ~250 kg and a required power of ~240 W. Such instrumentation
allows a unique, unprecedented and very powerful combination of large field of
view (3-4 sr), a broad energy energy band extending from ~1 keV up to ~20 MeV,
an energy resolution as good as ~300 eV in the 1-30 keV energy range, a source
location accuracy of ~1 arcmin. The mission profile included a launch (e.g., by
Vega) into a low Earth orbit, a baseline sky scanning mode plus pointed
observations of regions of particular interest, data transmission to ground via
X-band (4.8 Gb/orbit, Alcantara and Malindi ground stations), and prompt
transmission of GRB / transient triggers.Comment: 13 pages, 8 figures, published in International Journal of Modern
Physics
Application of biotic and taxonomic distinctness indices in assessing the Ecological Quality Status of two coastal lakes: Caprolace and Fogliano lakes (Central Italy)
Marine biotic indices (AMBI, BENTIX) and the statistical tool M-AMBI (Multivariate AMBI) were applied as a comparative approach in assessing the Ecological Quality Status (EcoQS) of two Mediterranean coastal lakes (Caprolace and Fogliano lakes) situated in the Circeo National Park (Central Italy). The macrobenthic community was analysed using univariate indices (community structure), correspondence analysis (CA) and taxonomic distinctness indices (Delta(+) and Lambda(+)). The community composition showed a dominance of lagoonal species in both coastal lakes, while in Caprolace lake marine taxa were also found. Diversity index (H') complies to ranges found in Mediterranean lagoons and taxonomic distinctness indices demonstrated that taxonomy structure is in accordance with natural variability ranges. Principal component analysis (PCA) on chemical parameters of water and sediment showed that both coastal lakes differ mainly in their organic matter composition. In fact, the protein fraction of bio-polymeric carbon prevails in Fogliano lake, while the 'refractory' component represented by carbohydrate fraction is predominant in Caprolace lake. The difference between the two coastal lakes was also demonstrated by co-inertia analysis (COIA) performed using abundance of species and concentrations of chemical parameters. The results from the application of the three biotic indices do not highlight a clear distinction between the two lagoons. However, the AMBI index provided a more suitable evaluation of EcoQS corresponding to 'slightly polluted' lagoons while M-AMBI and moreover BENTIX indices indicated a worsening situation. The biotic indices are widely used in assessing the EcoQS in marine environments, but their proper application in transitional waters would depend on a resettlement; thresholds established in the biotic index scale values need to be modified according to natural variability of transitional waters referring to abiotic conditions and abundance of tolerant species. (C) 2008 Elsevier Ltd. All rights reserved
Fundamental Physics with the Laser Astrometric Test Of Relativity
The Laser Astrometric Test Of Relativity (LATOR) is a joint European-U.S.
Michelson-Morley-type experiment designed to test the pure tensor metric nature
of gravitation - a fundamental postulate of Einstein's theory of general
relativity. By using a combination of independent time-series of highly
accurate gravitational deflection of light in the immediate proximity to the
Sun, along with measurements of the Shapiro time delay on interplanetary scales
(to a precision respectively better than 0.1 picoradians and 1 cm), LATOR will
significantly improve our knowledge of relativistic gravity. The primary
mission objective is to i) measure the key post-Newtonian Eddington parameter
\gamma with accuracy of a part in 10^9. (1-\gamma) is a direct measure for
presence of a new interaction in gravitational theory, and, in its search,
LATOR goes a factor 30,000 beyond the present best result, Cassini's 2003 test.
The mission will also provide: ii) first measurement of gravity's non-linear
effects on light to ~0.01% accuracy; including both the Eddington \beta
parameter and also the spatial metric's 2nd order potential contribution (never
measured before); iii) direct measurement of the solar quadrupole moment J2
(currently unavailable) to accuracy of a part in 200 of its expected size; iv)
direct measurement of the "frame-dragging" effect on light by the Sun's
gravitomagnetic field, to 1% accuracy. LATOR's primary measurement pushes to
unprecedented accuracy the search for cosmologically relevant scalar-tensor
theories of gravity by looking for a remnant scalar field in today's solar
system. We discuss the mission design of this proposed experiment.Comment: 8 pages, 9 figures; invited talk given at the 2005 ESLAB Symposium
"Trends in Space Science and Cosmic Vision 2020," 19-21 April 2005, ESTEC,
Noodrwijk, The Netherland
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